3. ВАЛИУЛЛОВА, менеджер по маркетингу технических решений компании Ericsson, И. ПАВЛОВ, старший менеджер по разработке решений Ericsson
Успешное внедрение новых прибыльных сервисов зависит как минимум от их привлекательности, простоты подключения и использования услуги абонентом, а также от подготовленности сетевой инфраструктуры оператора.
С одной стороны, появление новых услуг (например, triple play) означает новые требования к технологической базе сети, с другой - экономичная, безопасная и высокопроизводительная сеть является основой для наращивания номенклатуры сервисов. В свою очередь, широкая палитра услуг и сложная распределенная сеть, в которой они предоставляются, налагают жесткие требования на такие важные сетевые аспекты, как безопасность, авторизованное использование ресурсов, гибкость управления и предоставления услуг.
Весь упомянутый комплекс требований привел компанию Ericsson к созданию пакета решений на основе концепции Public Ethernet, сочетающего экономичность для пользователя, возможность гибкого расширения и предоставления услуг для оператора и необходимый уровень безопасности для всех.
Благодаря совместимости с IP, простоте развертывания и, что важнее всего, оптимальному соотношению цена/производительность Ethernet выходит на первое место как основной стандарт среди технологий доступа. Однако в том виде, в каком Ethernet существует в корпоративных средах, он не отвечает требованиям к СОП. Сеть с широкополосным доступом, где услуги предоставляются в режиме реального времени, должна поддерживать масштабирование для одновременного обслуживания большого числа пользователей и дифференцированные сервисы, предоставлять обслуживание высочайшего качества, обеспечивать безопасное соединение.
Масштабируемость и доступ
Ключ к успеху оператора в условиях жесткой конкуренции - снижение цены на существующие услуги и внедрение новых, прибыльных, услуг. Узел Ethernet DSL-Access (EDA) компании Ericsson, входящий в решение Public Ethernet, значительно снижает начальные капитальные затраты. Высокая масштабируемость и применение технологии Ethernet делают IP DSLAM комплексной системой, обеспечивающей поэтапное расширение (добавление 10-12 пользователей за один этап). Систему EDA можно наращивать линейно, развертывая как малые узлы (на десятки абонентов), так и емкостью в тысячи линий.
При выборе технологии доступа на «последней миле» сети оператор должен учитывать характеристики инфраструктуры (существующей или потенциальной), профиль абонентов и предлагаемые им услуги. Использование в сети Public Ethernet различных вариантов построения сегмента абонентского доступа (xDSL по медной паре, медные или оптические линии Ethernet, доступ WLAN) позволяет оператору в каждом конкретном случае наиболее экономично решать эту задачу (рис. 2).
Безопасность и разделение пользователей
LAN, до последнего времени практически единственная среда приложения Ethernet, определяется как единая область трансляции. Поэтому, когда один пользователь передает информацию по LAN, ее получают все пользователи сети. Стандарт виртуальной LAN (VLAN), описанный в IEEE 802.1Q, является продолжением стандарта Ethernet, который определяет способы логической сегментации LAN на различные области трансляции уровня 2. Поскольку оег-ментация выполняется логически, конечным пользователям не обязательно физически находиться в одном месте.
В домашних сетях VIAN используется для разделения предоставления услуг. Чтобы предупредить несанкционированный доступ к услугам, пользователей подключают только к тем сервисным VLAN, к которым они приписаны (рис. 3). Таким образом, пользователи, имеющие доступ к одним и тем же сервисным VLAN, фактически подключены к одной области трансляции. Следствием этого являются две основные проблемы:
во-первых, конечные пользователи, подключенные к одной сервисной VLAN, могут устанавливать одноранговые соединения на уровне 2, минуя сервер широкополосного удаленного доступа (BRAS), который контролирует доступ, обеспечивает систему безопасности, управляет биллингом и распределяет ресурсы;
во-вторых, злонамеренный пользователь имеет возможность производить специфические атаки на других пользователей уровня 2.
Решение Public Ethernet от Ericsson устраняет эти проблемы. Обработка уровня 2 между устройствами конечных пользователей требует знания адреса однорангового узла этого уровня или адреса управления доступом в сеть (МАС-адрес). Устройства получают МАС-адрес других устройств, посылая запрос протокола разрешения адресов (ARP). Чтобы, не допустив этого, направить весь поток данных от абонентов к BRAS, на узле доступа Ethernet есть механизм принудительной переадресации MAC. Прокси-сервер ARP в составе узла доступа не позволяет пользователям отправлять в сеть многоадресные запросы, выдавая в ответ только МАС-адрес BRAS. Таким образом, весь трафик конечных пользователей принудительно перенаправляется в BRAS.
В случае доступа «точка-точка» (РРР) протокол РРР через Ethernet (PPPoE) создает отделенные друг от друга РРР-туннели между каждым устройством пользователя и BRAS. Поскольку узел доступа Ethernet принимает исключительно кадры РРРоЕ, поток данных от абонента может поступать только на BRAS.
В бизнес-сетях VLAN может быть выделен для одного пользователя (сеть филиала компании, регионального или корпоративного офиса) с целью создания изолированной сети уровня 2, которая может пересекаться с магистральной IP-сетью в VPN уровня 2 или 3. Трафик,, который поступает от корпоративной интранет-сети, эмуляции каналов в сети IP (CESoIP) для офисной АТС или ретрансляции кадров, проходит по сети уровня 2 беспрепятственно.
Список литературы
Журнал «ИнформКУРЬЕРСвязь» № 8, 2005 год.
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