Recommendations for E1 and T1 Access lines
Today we touch upon one of the best practices for E1 and T1 dedicated circuits or links which we are usually used in the WAN. We have so many recommendations and designs across it. We always think that if we have the requirement like 64 Kbps of WAN circuit which we taken from the ISP side what will be the interface type and which router we are going to have for this kind of interfaces.
We always have different designs and recommendations as per the network requirements. Some of them are very large network where we uses Ethernet interfaces with high bandwidth WAN speed and we can choose the router as per the capability of the WAN bandwidth. You can use various models of Cisco, Juniper or Huawei routers in your network.
Now we have some clarity of the interfaces types it can be dedicated or Ethernet types of interfaces. We all know about the ethernet interfaces but there are always confusion around the dedicated links across the people.
There are two types of dedicated circuits and they are E1 and T1. These are actually depends in which country you are living in. As if i am talking about Japan and Americas, they always uses T1 dedicated circuits and the rest of the world uses E1 dedicated circuits.
Lets start with the recommendations of these circuits in details. First of all we will discuss on E1 WAN circuits and then we can have discussion on T1 dedicated circuits.
Recommendations for E1
We always have different designs and recommendations as per the network requirements. Some of them are very large network where we uses Ethernet interfaces with high bandwidth WAN speed and we can choose the router as per the capability of the WAN bandwidth. You can use various models of Cisco, Juniper or Huawei routers in your network.
Now we have some clarity of the interfaces types it can be dedicated or Ethernet types of interfaces. We all know about the ethernet interfaces but there are always confusion around the dedicated links across the people.
There are two types of dedicated circuits and they are E1 and T1. These are actually depends in which country you are living in. As if i am talking about Japan and Americas, they always uses T1 dedicated circuits and the rest of the world uses E1 dedicated circuits.
Lets start with the recommendations of these circuits in details. First of all we will discuss on E1 WAN circuits and then we can have discussion on T1 dedicated circuits.
Recommendations for E1
To allow easy increase in port speeds or where cost effective, customers may be offered a sub rate E1 port (64kbps, 128kbps, 256kbps, 384kbps, 512kbps, 786kbps, 1024kbps and 1536kbps) over a clear E1 access, G.704 framing allows the appropriate number of timeslots to be selected to provide the required port speed.
Most access providers will provide a G.703 presentation but there are two variants:
- 75Ohm (Unbalanced)
- 120Ohm (Balanced)
The correct interface type – 75 or 120 Ohm – needs to be specified to order the correct cable with the CPE.
 |
| Fig 1.1- E1 Standard Circuits |
The problem arises that, even within one country, the standard adopted by the PTT and alternative access providers is often different. If an order is placed on Orion for one access provider, and as a result of an escalation the access provider is changed, then the CPE would be delivered as per the original order. This could result in the CPE being incompatible with the interface provided by the alternative access provider.
In order to avoid the problem and ensure that the service delivery of access and CPE goes as smoothly as possible, the IP Connect Global Product Line recommends the following for Cisco routers:
The default standard for E1 access is G.703 presentation is 120 Ohm (Balanced) with a RJ-45 interface irrespective of the presentation offered by the access provider. Therefore the CPE should always be ordered with a Balanced 120 Ohm card (Cisco x9xxx – (VWIC3-xMFT-T1/E1), PA-MC-2E1/120 or PA-MC-8TE1+, Cisco ISR4xxx (NIM-1MFT-T1/E1) depending on CPE type)
A Balanced-Unbalanced converter cable should be included with every order for 2048kbps access. The product name is: 75 to 120 Ohm adaptor cable (CAB-E1-RJ45BNC). The additional cost of the Balanced-Unbalanced converter cable is typically under 2 Euros/Dollars per month if a 3 year CPE contract is chosen.
Recommendations for T1
T1 interfaces are always 100 Ohm Framed.
Product Line Bundled CPE recommendation is T1 modules with RJ-48C interfaces and an internal CSU/DSU, such as the HWIC-1DSU-T1 card. If there is a requirement for FRF16.1 at later stages, it is recommended to use the VWIC3-2MFT-T1/E1 (Cisco x9xx) or NIM-1MFT-T1/E1 (Cisco 4xxx), which also has an internal CSU/DSU, therefore can be used as an alternative to the HWIC-1DSU-T1.
 |
| Fig 1.2 T1 Dedicated Circuits |
Alternatively a separate CSU/DSU may be used, BT recommend Quick Eagle CSU/DSU, these present a V.35 interface which is compatible with the Cisco HWIC-1T card (Cisco x9xxx) and a V.35 cable (CAB-SS-V35MT)
