|
Designed for synchronous services that require locked clocks; in effect a “leased line” over Ethernet and IP packet networks.
- The PacketBand-VX provides reliable, transparent and manageable end-to-end X.21 and V.35 connectivity across Ethernet and IP packet networks. It can connect to local devices and/or leased lines and is able to provide, take and recover clocks.
- Circuits can be established 24/7 or in response to requests from the attached equipment via control signals so the circuit is established periodically and on-demand.
- PacketBand also supports Multicast across the Ethernet/IP networks for simplex broadcast applications.
- Clocks are recovered extremely accurately and can exceed the G.823 Synchronous Interface requirement which is used extensively as the quality guide-line for leased lines.
Connectivity Overview
- PacketBand-VX supplies a clear or transparent serial clock-recovered or synchronous “pipe” at speeds of 64kbps to 2.048Mbps across different types of packet networks. It duplicates a traditionally-delivered X.21 or V.35 carrier leased line but uses low-cost and widely available packet networks as the transport medium.
- To generate the correct V.35 and X.21 circuits over Ethernet and IP networks, clocks can be generated from one PacketBand and recovered by the other, ensuring synchronisation and no data slips.
- This configuration provides synchronised clocks to both ends of the circuit when there is no available clock source at the customer premises. This is a common situation when replacing X.21 and V.35 leased lines as these will have normally provided clock from the carrier’s local).
- PacketBand can also source clocks in these instances from a centrally located Multicast source.
- Or clock can be supplied by the CPE / DTE or leased line.
Control Signal Dialling
- The PacketBand delivers a circuit 24/7 but optionally has the ability to establish the V.35 over Ethernet or X.21 over Ethernet link in response to a DTE raising a control lead.
- This feature means network capacity is only used when required by the DTE /application.
Multicast
- PacketBand has the unique feature of supporting Multicast transmission which has three key advantages.
- Multicast is an efficient method of transporting unidirectional (simplex) traffic from one main transmission location to multiple remote sites. PacketBand has the ability to transmit to a Multicast-enabled router and for remote PacketBands to “join” Multicast groups.
- This optional facility, together with the PacketBand’s excellent clock recovery accuracy, makes the system ideal for broadcast applications.
- The Multicast capability also means that the PacketBand can separate the clock recovery data from the bulk user data. This means larger networks with multiple “hops” can deliver not only improved clock synchronisation, but there are network design/loading/QoS and resiliency benefits as well.
- X.21 and V.35 leased lines are normally provided with the clock coming from the carrier network. The Multicast feature means all customer sites can be easily synchronised, particularly where no clock source is available at the end user site.
- When delivering clocked services to customer sites the Multicast feature ensures all customer sites are clock-locked/synchronised. This is covered more extensively in the PacketBand-TDM-1MC and PacketBand-TDM-3MC brochures.
Central Site
- Many X.21/V.35 applications use a channelised G.704 device at the central site to reduce interface and other costs.
- Using the PacketBand-VX at remote locations together with a “Grooming” version of the PacketBand-TDM-D range means this scenario can also be replicated over packet networks.
Clocking
- Clocking and clock-recovery is a critical area for this type of V.35 X.21 TDM over Ethernet technology and one in which the whole PacketBand range excels.
- The method of clock recovery (patent pending) uses a variety of methods depending upon the network type. These work in conjunction with a number of sophisticated intelligent algorithms which calculate any necessary adjustments to the clock based on an algorithm. These algorithms allow users to “tune” the clock recovery to the characteristics of the packet network.
- Across a managed high-quality network, PacketBand can exceed the G.823 mask for Synchronisation. Graphs on performance under different circumstances against specifications are available on this web site and upon request.
Oscillators
- The quality of the oscillator when recovering the clock across the packet network is very important and the PacketBand-VX supports a number of options.
Network Types
- PacketBand-VX can run over a variety of different networks, from the best with management and QoS to the public Internet at the opposite extreme. As a general rule, the better the network the better the circuit delivered by PacketBand.
Ethernet and Packet Handling
- Support for 10/100/1GE.
- Support for packets up to 1632 bytes in size (10,240 bytes Mar 09).
Prioritisation
- TDM packets can be assigned IP Diffserv ( DSCP ) or ToS and 802.1p CoS values.
- PacketBand supports full 802.1q tagging and the associated 802.1p CoS prioritisation levels.
- All egress packets including TDM links can be prioritised across four output queues using CoS (802.1p) or Diffserv/ToS values.
VLAN Handling
- PacketBand’s powerful and latest-generation on-board packet switch offers advanced 802.1Q VLAN facilities such as multiple TAGing, TAG insertion/removal, port routing based on default TAG or a Global TAG table.
Link Aggregation Control Protocol (LACP)
- This feature enables two or more Ethernet ports connected between PacketBand and the network switch to be aggregated together. This aggregation makes it appear as if the multiple links are acting as a single high capacity circuit. Furthermore, it adds a level of redundancy with automatic rerouting. See the TDM-1E Application Overview for further information.
Rapid Spanning Tree Protocol (RSTP)
- RSTP identifies the means to build an Ethernet network which contains physical loops between bridges. This facility enables PacketBands to be connected to more than one network switch via different circuits and to provide an automatic fall-back in the case of a link failure. This is covered in more detail in the PacketBand-TDM-1E Application Overview.
Rate Limiting
- Individual packet ports can have the traffic capacity restricted in various ways, even though the access is 10/100/1GE. This is particularly useful on the second Ethernet port when connected to user LANs where the main link to the network could be “swamped” by data from attached devices.
PDV (Packet Delay Variation or jitter)
- The PacketBand-TDM-VX supports up to 400mseconds of PDV or jitter depending upon configuration parameters. This is normally far in excess of the PDV experienced on private networks and many Internet connections.
- The jitter buffer can be set in msec granularity and adjusted manually or automatically whilst the circuit is in place, overcoming ‘skew’ at start up time caused by the first packet in the buffer arriving later or earlier than average.
Overheads
- Overheads are very small but the total overhead as a percentage of the payload depends upon a number of factors. PacketBand supports a number of different packet network protocols. The user’s choice for a particular network will be constrained by the network infrastructure. Each packet transmitted consists of Ethernet packet headers and protocol packet headers.
- PacketBand overheads are very low but the size of the packet does affect the bandwidth needed. Large packets have a high payload as a percentage of the fixed overhead so tend to be more efficient. But they do take slightly longer to "build" and a lost larger packet obviously has more data within it.
- Patapsco have available a spreadsheet which identifies overhead percentages and latency under different settings. Please contact Patapsco or your supplier.
Latency
The total end-to-end latency experienced between two X21/V.35 devices using PacketBands is made up of four elements:
- Processing Delay
The latency or processing delay through each PacketBand is optimised to be as low as possible. Typical processing delay is less than 1msec.
- Transmit Delay
This is the time necessary to wait for sufficient incoming data to arrive from the attached device so a packet of the configured size can be built and transmitted over the network. This is typically around the 1msec range.
- Jitter
Packet network networks differ in how consistently packets pass though them; some packets take more or less time than the average. PacketBand provides a synchronous clocked circuit to the attached devices and therefore has to have data ready and available for the relevant clock pulse. PacketBand buffers the fast packets so as to ensure the slow ones can arrive in time to be used. The amount of buffering is user-configurable and will depend upon the performance of the network. Note that this buffering is only required on the PacketBand receive data path and the amount of buffering needed (which equates to latency) is a result of the network, not PacketBand.
- Transit Delay
All IP networks have different average transit delays. These vary depending upon a large number of criteria, including the number of “hops” and whether satellites are involved. Typically, domestic links are very fast, inter-continental around 60msec and a satellite can add 250msecs. Please consult your network supplier.
- Summary:
Between any pair of PacketBands on a terrestrial network, the most significant element contributing to latency is size of the Jitter Buffer (which is user configurable). This is directly dependant on the performance of the network and outside the control of PacketBand.
Management
- PacketBand can be locally or remotely configured using Patapsco’s easy-to-use high functionality DbManager GUI software.
- DbLite is supplied free with each unit.
- Optionally available are different versions to support requirements for larger or more integrated networks. It is sophisticated but simple to use via an intuitive Graphical User Interface (GUI) which controls, configures and monitors individual Patapsco units and complete networks, allowing control and visibility of a network of PacketBands and links, and has capabilities such as SNMP Traps & Alarms and continuous polling of devices. A document identifying the differences between DbLite and other versions is available.
- Used by various organisations with different network sizes - up to and including carriers - versions of DbManager deliver a network wide view of all PacketBands and links via a 4-layer “tree-structured” overview. The status of all PacketBands and links are easy to identify with Alarms being colour coded and passed up the tree.
- More information is available in the downloadable PDFs on this page.
- The PacketBand-VX delivers highly reliable and accurately clocked V.35 and X.21 services over Ethernet and IP networks. Please contact us to discuss your requirements.
Further details and specifications are available in the PDFs at the Top of this page and when registered. |
