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What is TDM over IP, Circuit Emulation, backhaul or Pseudo Wire?
Many carriers and customers are moving to Packet Networks, reaping the benefits of a single low cost voice/data delivery method. Handling mainly router-based data traffic and compressed voice over IP (VoIP), network costs are usually significantly reduced with the added advantage of a single infrastructure to install, train staff on and managed.

But, what about those network devices that cannot run over native IP?
These include most synchronous clocked equipment using T1/E1 clear or channelised services, X.21 and V.35. The issues here are largely to do with clocking and synchronization and making sure the data is received as-and-when required. This is particularly true in some markets, such as the mobile GSM/CDMA BTS cellular backhaul market where clocks and synchronisation is key. In fact, most devices that use E1s and T1s are sensitive to clocking, its accuracy and its stability.

Delivering E1/T1 services across new IP-based radio/microwave links also opens new low-cost service methods.

But, what about customers who do not have an IP-PBX or to whom the quality and delay issues associated with VoIP are unacceptable for their particular application? How can they gain the cost advantages of IP without the quality loss or major upgrade investments?

Or a customer who wants to migrate from a legacy-based network to an IP one over a period of time and still have an overall system that uses IP and inter-connects properly?

Patapsco’s PacketBand range can help with all of these requirements, and more. Models within the range offer TDM over IP, also called TDM Pseudo Wires or CESoIP. These are circuits that look like a synchronous leased line but which actually use a Packet Network, or even Internet. They can be established with different amounts of bandwidth at different times of the day.

The sophisticated but easy-to-use PacketBand range means legacy products and other equipment that need G.703/4, T1 and X.21/V.35 devices can now be delivered over IP with easy, confidence, manageability and visibility.

Clocks are the Key !!
The core basis of this technology is the ability to recover a clock across the non-clocked asynchronous Packet Network so both "ends" think they are synchronised to one source and running over a traditional leased line.

Unless this can be done accurately and reliably over a long period, particularly with dynamically changing loads on the Packet Network, the end devices will see slips which means data loss and errors.

One of PacketBand-TDM's key strength is its ability to recover clocks quickly; to a very high accuracy and stability; and to be robust and reliable should there be issues on the network.

Both MTIE and TIE G.823 PDH synchronisation masks (used as the reference for leased line quality) can normally be met, with clock accuracy down to 20-50ppb (parts per billion) and with very small step-changes in any clock speed.

[Note that other vendors quote “G.823” but this is generally either not for a clock-recovered system or it often only the Immunity to Jitter element of G.823 not the quality of the generated clock. Furthermore, inferior products will often only manage to recover a clock to 20-50ppm (parts per million) or up to 1,000 times worse than PacketBand and be very unstable at the same time!]

Every Packet Network is different and PacketBand benefits from a choice of software algorithms which optimise performance for different environments and characteristics. Different networks will deliver different qualities of clock; a quality managed network will provide quite different results from the public Internet.

PacketBand can provide a high quality clocked system over a wide range of networks types.